Communication system and its method

ABSTRACT

In a communication system including a plurality of pairs of a transmitting device  2  and a receiving device  3 , the transmission performance in the pairs is to be improved. The transmitting device  2 - k  transmits a transmission signal s k (t) to the receiving device  3 - k  a plurality of number of times. The receiving device  3 - k  updates the weight matrix W k  and the hopping pattern P k  used by the FIR filter which performs filtering on the transmission signal r k (t) at a predetermined time interval. The receiving device  3 - k  transmits the updated hopping pattern P k  to the transmitting device  2 - k . The transmitting device  2 - k  receives the hopping pattern P k  to be used for subsequent spread spectrum.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. national stage application claimingthe benefit of International Application No. PCT/JP2008/062753, filed onJul. 15, 2008, which claims the benefit of Japanese Application No.2007-341948, filed on Dec. 25, 2007, the entire contents of which areincorporated herein by reference in their entireties.

TECHNICAL FIELD

The present invention relates to a communication system and its methodfor transmitting data in a spread spectrum system using frequencyhopping.

BACKGROUND ART

For example, Non-Patent Document 1 discloses a communication systemconfigured such that any two communication devices are taken from alarge number of communication devices to make a plurality of pairs ofcommunication devices, each pair capable of transmitting data in anasynchronous DS-CDMA (Direct-Sequence Code Division Multiple Access)system.

Non-Patent Document 2 discloses a communication system where a receivingdevice feeds back a hopping pattern to a transmitting device.

Non-Patent Document 3 discloses an initial value of the hopping patternP.

[Non-Patent Document 1]: Asynchronous Decentralized DS-CDMA UsingFeedback-Control Spreading Sequences for Time-Dispersive Channels,(Kazuki CHIBA, Masanori HAMAMURA and Shin'ichi TACHIKAWA, IEICE TRANSCOMMUN, VOL. E91-μ, NO1. JANUARY 2008, PAPER, Special Section onCognitive Radio and Spectrum Sharing Technology, The Institute ofElectronics, Information and Communication Engineers)[Non-Patent Document 2]: Interactive constructions of optimum signaturesequence sets in synchronous CDMA systems, (S. Ulukus et. al., IEEETrans. Inform., Theory, vol. 47, no. 5, pp. 1989-1998, July 2001)[Non-Patent Document 3]: Address assignment for a time-frequency-codedspread-spectrum system (G. Einarson, Bell Syst. Tech. J., vol. 59, no.7, pp. 1241-1255, September 1980)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Against the above background, the communication system and its methodaccording to the present application has been made, and one of theembodiments is a communication system (1) including a plurality of pairsof a transmitting device (2) and a receiving device (3), wherein in eachof the pairs, the transmitting device has signal transmission units(222, 224, 226, and 244) which, based on a spread pattern (hoppingpattern P_(k)) which includes a plurality of first elements (weights)defined with respect to components of a predetermined first number (M)of first domains (frequency domains) and components of a predeterminedsecond number (L) of second domains (time domains) and spreadstransmission data (message symbol b_(k)) to the components of the firstdomains and the components of the second domains, sequentially spreadsthe transmission data to the components of the first domains and thecomponents of the second domains every predetermined time interval(T_(c), and T_(s)) and transmits the transmission data as a transmissionsignal (s_(k)); and update units (240 and 242) which, based on thespread pattern received from the receiving device, update the spreadpattern used to spread the transmission data; and the receiving devicehas receiving units (208, 210, 212) which receive the transmissionsignal; expansion units (400, 402, 404, 424, and 440) which sequentiallyexpand the received transmission signal (s′_(k)) into a plurality ofsecond elements defined with respect to components of the first domainswhose number is equal to or greater than the first number and componentsof the second domains whose number is a third number (L+α) which isgreater than the second number at each of the time intervals; processingunits (410, 414, 428, 442, 444) which sequentially perform a processusing a plurality of first coefficients defined for each of the secondelements on the second elements obtained as a result of the expansion ateach of the time intervals; a generation unit (344) which generates thespread pattern using the processed second elements and a plurality ofsecond coefficients constituting a part of the first coefficients; and apattern transmission unit (346) which transmits the generated spreadpattern to the transmitting device.

It should be noted that the above description contains referencenumerals to clarity the correspondence between the present specificationand the accompanying drawings, which is not intended to limit thetechnical scope of the present invention.

SUMMARY

An embodiment of the communication system according to the presentinvention includes a large number of communication devices and uses anyplurality of pairs of the communication devices (e.g., a pair of twocommunication devices) to transmit a transmission signal obtained byspreading transmission data based on a hopping pattern represented in amatrix form, at the same time in parallel between the pairs ofcommunication devices.

The plurality of pairs of communication devices can share the same pathwith each other. Thus, a pair of communication devices receives atransmission signal from another pair of communication devices, whichdecreases the transmission quality of the transmission signal in thepair communication devices.

In a pair of communication devices, one communication device(transmitting device) mainly transmits a transmission signal and theother communication device (receiving device) receives the transmissionsignal. It should be noted that the transmitting device and thereceiving device may be of a completely different configuration or ofthe same configuration.

The receiving device receives a transmission signal, expands thereceived transmission signal into a matrix of components of a frequencydomain and components of a time domain, multiplies each of the expandedmatrix elements by a coefficient (first coefficient) for filtering, addsthem in a row direction and in a column direction, and then outputs themas the filtering results.

The first coefficient uses the first coefficient as an element and canbe expressed in a matrix larger in the row direction and in the columndirection or in any one of the directions than that of the frequencyhopping pattern.

The receiving device uses the above filtering results to update thematrix of the first coefficients so as to improve the quality of thetransmission data decoded from the transmission signal.

Further, the receiving device extracts the second coefficientscorresponding to the hopping pattern from the updated matrix of thefirst coefficients and transmits them to the transmitting device.

The transmitting device uses a new hopping pattern transmitted from thereceiving device, generates a transmission signal with a transmissionperformance better than that before the new hopping pattern is used, andtransmits the signal to the receiving device.

Thus, while transmission and feedback of transmission signals arerepeated between the transmitting device and the receiving devicebelonging to the same pair of communication devices, the signaltransmission performance therebetween is gradually improved.

The technical advantages of the present invention and other technicaladvantages should be readily apparent to those skilled in the art byreading the detailed description of the embodiments illustrated in theaccompanying drawings.

The accompanying drawings are incorporated in the present specificationto constitute a part thereof, illustrate embodiments of the presentinvention, and serve to explain the embodiments as well as the principleof the present invention.

The drawings referred to in the present specification should not beunderstood to be drawn in a certain scale unless otherwise noted.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the present invention should be most readilyunderstood by referring to the following description as well as theaccompanying drawings regarding the configuration and the operationthereof.

FIG. 1 illustrates a communication system according to an embodiment ofthe present invention;

FIG. 2 illustrates modeled transmission signals s′k(t) received by areceiving device of the communication system illustrated in FIG. 1 and ahopping pattern fed back from the receiving device to a transmittingdevice;

FIG. 3 illustrates a hardware configuration of the transmitting deviceand the receiving device illustrated in FIG. 1;

FIG. 4 illustrates a configuration of a transmitting program executed bythe transmitting device and the receiving device illustrated in FIG. 1;

FIG. 5 illustrates a configuration of a symbol and a chip used by thetransmitting device and the receiving device;

FIG. 6 illustrates a configuration of a receiving program executed bythe transmitting device and the receiving device illustrated in FIG. 1;

FIG. 7 illustrates a configuration of a filter unit of the receivingprogram illustrated in FIG. 6;

FIG. 8 illustrates a configuration of the coefficient multiplicationunit illustrated in FIG. 7;

FIG. 9 illustrates a communication sequence diagram illustrating datatransmission and feedback (S10) of the hopping pattern P_(k) between thetransmitting device and the receiving device illustrated in FIG. 1 andthe like;

FIG. 10 illustrates a model of a path for evaluating the performance ofthe communication system;

FIG. 11 is a graph of bit error rate performance with respect to thenumber of active transmission signals s_(k)(t) in the communicationsystem;

FIG. 12 is a graph of bit error rate performance with respect toE_(b)/N_(o) for K=32; and

FIGS. 13A to 13D each are a graph illustrating an initial hoppingpattern, the updated hopping pattern, and the corresponding powerspectra.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail.

The embodiments of the present invention are illustrated in theaccompanying drawings.

The present invention is described in connection with the embodiments,but it should be understood by those skilled in the art that thedescription herein of specific embodiments is not intended to limit theinvention to the particular forms disclosed.

On the contrary, the present invention is intended to cover the explicitspirit as defined by the appended claims as well as all alternatives,modifications, and equivalents falling within the scope of the inventionas defined by the appended claims.

Moreover, the present invention is described specifically as well as indetail to the level that those skilled in the art can sufficientlyunderstand the appended claims.

However, as will be apparent to those skilled in the art, the presentinvention may be made without following all the descriptions describedspecifically as well as in detail herein.

It should be noted that known methods, procedures, components, andcircuits may not be described in detail for a simplified description ofthe embodiments of the present invention.

However, it should be noted that these terms and other similar termsshould each be associated with an appropriate physical quantity and thusshould be understood as a convenient label assigned to the correspondingquantity.

As will be apparent from the above discussion that unless otherwisenoted, throughout the present invention, the description containing theterms such as “spread” and “transmit” should be understood to mean anoperation and a process executed by a specific use of a computerhardware resource or a dedicated hardware resource.

[Communication System 1]

First, a communication system 1 according to an embodiment of thepresent invention will be described.

FIG. 1 illustrates the communication system 1 according to an embodimentof the present invention.

As illustrated in FIG. 1, the communication system 1 includes a K (twoor more integer) number of transmitting devices (TX) 2-1 to 2-K and a Knumber of receiving devices (RX) 3-1 to 3-K each of which is fixed orsemifixed in one place or mobile.

In the following description, when any one of the plurality ofcomponents such as transmitting devices 2-1 to 2-K is specified withoutidentifying a specific one, the one may be written simply as thetransmitting device 2 for simplicity.

Hereinafter, the same reference numeral or reference character denotessubstantially the same component throughout the figures.

Note that the transmitting device 2 and the receiving device 3 may be ofthe same configuration, but are distinguished from each other in thefollowing description for the purpose of substantiating and clarifyingthe description.

As described above, the communication system 1 is configured such thatone transmitting device 2 may transmit a transmission signal to aplurality of receiving devices 3, a plurality of transmitting devices 2may each transmit a transmission signal to one receiving device 3, and aplurality of transmitting devices 2 may each transmit a transmissionsignal to a plurality of receiving devices 3.

However, in the following description, for the purpose of substantiatingand clarifying the description, the communication system 1 is configuredas a specific example such that one transmitting device 2-k (K≧k≧1) andone receiving device 3-k are paired and a transmission signal istransmitted only between the transmitting device 2-k and the receivingdevice 3-k included in each of the plurality of pairs; and based on afrequency hopping pattern, spread spectrum is performed on thetransmission signal s_(k)(t) expressed in the low-pass equivalent.

FIG. 2 illustrates modeled transmission signals s′_(k)(t) received bythe receiving device 3-k of the communication system 1 illustrated inFIG. 1 and the hopping pattern fed back from the receiving device 3-k tothe transmitting device 2-k.

The communication system 1 allows a path to be shared by not only a pairof the transmitting device 2-k and the receiving device 3-k but alsoother pairs.

In this case, as illustrated in FIG. 2, the receiving device 3-kreceives not only the transmission signal s_(k)(t) from the transmittingdevice 2-k included in the same pair but also transmission signalss′_(k)(t) including the transmission signals from the transmittingdevices 2-1 to 2-(k−1) and 2-(k+1) to 2-K included in other pairs.

In other words, the communication system 1 allows the receiving device3-k to be constantly susceptible to interference from each of thetransmitting devices 2-k′ belonging to other pairs.

Even in such a circumstance, the receiving device 3-k of thecommunication system 1 sequentially updates a weight matrix (W_(k))expressed in complex weights w_(k, m), and _(l) (M≧m≧1 and L+α≧l≧1,where α is an integer equal to or greater than 0 and l is a process foreach chip time length T_(c)) used for filtering so as to improvereceiving performance of the transmission signal s_(k)(t) received fromthe transmitting device 2-k belonging the same pair.

Further, the receiving device 3-k feeds back a part of the elements ofthe updated weight matrix (W_(k)) to the transmitting device 2-k as ahopping pattern P_(k) and causes the transmitting device 2-k to updatethe hopping pattern used for spectrum spreading so that the transmissionsignal s_(k)(t) itself can be subject to spectrum spreading using apattern suitable for passing through the path illustrated in FIG. 2.

[Hardware Configuration]

FIG. 3 illustrates a hardware configuration of the transmitting device 2and the receiving device 3 illustrated in FIG. 1.

As illustrated in FIG. 3, the transmitting device 2 and the receivingdevice 3 are used by being connected to a computer (PC) or a network(not illustrated) such as a LAN where a message symbol (transmissiondata) b_(k) (n: n denotes the sequence of message symbols) in a QPSK(quadrature phase-shift keying) system is outputted to the transmittingdevice 2 or the message symbol b_(k)(n) is inputted from the receivingdevice 3.

The transmitting device 2 and the receiving device 3 include aninterface (IF) circuit 200, a digital signal processor (DSP) 202, amemory 204 for the DSP 202, a digital/analog (D/A) converter 206, aradio frequency (RF) circuit 208, an antenna 210, an analog/digital(A/D) converter 212, a CPU 214, and a memory 216 for the CPU 214, and auser interface (UI) device 218 interfacing between the transmittingdevice 2 or the receiving device 3 and the user.

The transmitting device 2 and the receiving device 3 include a componentsuch as a cell phone configured to be able to transmit voice and data inthe CDMA system or a radio LAN device serving as a computer allowingsoftware to perform signal processing, radio communication andinformation processing.

Note that in the following description, for the purpose ofsubstantiating and clarifying the description, it is assumed as aspecify example that the transmitting device 2 and the receiving device3 allow software to perform signal processing and informationprocessing.

However, the transmitting device 2 and the receiving device 3 may beconfigured to allow embedded hardware to perform signal processing andinformation processing depending on the configuration, application, andperformance requirement thereof.

Moreover, the transmitting device 2 and the receiving device 3 do notnecessarily use both the DSP 202 and the CPU 214, but may use either anyone depending on the configuration, application, and performancerequirement thereof.

In the transmitting device 2-k and the receiving device 3-k, the IF 200provides a function to input and output the message symbol b_(k)(n)between the computer or the network and the transmitting device 2 andthe receiving device 3.

The DSP 202 executes a signal processing program stored in the memory204 to perform spread spectrum on a message symbol b_(k)(n) inputtedfrom the IF 200 or a message symbol b_(k)(n) generated from the voiceinputted through a microphone (not illustrated) of the UI 218, andoutputs it to the D/A 206.

The D/A 206 converts the digital message symbol b_(k)(n) undergoingspread spectrum to an analog baseband or a transmission signal s_(k)(t)with an intermediate frequency of the frequency which can be processedby the DSP 202 or the CPU 214, and outputs it to the RF 208.

The RF 208 converts the transmission signal s_(k)(t) to a transmissionsignal s_(k)(t) of a frequency used for signal transmission between thetransmitting device 2 and the receiving device 3 and transmits thesignal to the path through the antenna 210.

Then, the RF 208 receives the transmission signal s_(k)(t) from thetransmitting device 2 or the receiving device 3 of the communicationparty, converts the signal to a transmission signal s_(k)(t) of abaseband or an intermediate frequency, and outputs the signal to the A/D212.

The A/D 212 converts the analog transmission signal s_(k)(t) to adigital transmission signal s_(k)(t) and outputs the signal to the DSP202.

The CPU 214 executes a program stored in the memory 216 to control theoperation of the transmitting device 2 and the receiving device 3, forexample, according to the user operation to the UI 218.

In addition, the CPU 214 performs processes of setting and updating theweight used for filtering the transmission signal s_(k)(t) received bythe DSP 202.

Moreover, the CPU 214 controls the UI 218 to present the user withinformation and the like.

[Software Configuration]

FIG. 4 illustrates a configuration of a transmitting program 20 executedby the transmitting device 2-k and the receiving device 3-k illustratedin FIG. 1.

FIG. 5 illustrates a configuration of a symbol and a chip used by thetransmitting device 2 and the receiving device 3.

As illustrated in FIG. 4, the transmitting program 22 includes a timingcontrol unit 220, first and second multiplication units 222 and 226, adelay unit 224, a hopping pattern (P_(k)) receiving unit 240, a hoppingpattern setting unit 242 and a frequency synthesizer (FS) unit 244.

The transmitting program 20 is supplied to the transmitting device 2 andthe receiving device 3, for example, via a storage medium or thenetwork; is loaded in the memory 204 for the DSP or loaded in the memory216 for the CPU illustrated in FIG. 3; and is executed by specificallyusing a hardware resource of the transmitting device 2 and the receivingdevice 3 under an OS such as ITRON executed by the DSP 202 or the CPU214 (the same is applied to the each of the following programs).

The transmitting program 22 uses the above units to perform spreadspectrum on the message symbol b_(k)(n) inputted through the network orthe like according to the hopping pattern to generate the transmissionsignal s_(k)(t) and outputs the signal to the D/A 206.

In the transmitting program 22 executed by the transmitting device 2-k,the timing control unit 220 controls the timing of the operation of eachcomponent of the transmitting program 22 so as to be synchronized withthe message symbol b_(k)(n) and the chip illustrated in FIG. 5.

The delay unit 224 gives a delay T_(s) of one message symbol to themultiplication result d_(k)(n−1) of an (n−1)-th message symbolb_(k)(n−1) outputted from the first multiplication unit 222.

When an n-th message symbol b_(k)(n) is inputted to the firstmultiplication unit 222, the delay unit 224 outputs the delayedmultiplication result to the first multiplication unit 222 as delay datad_(k)(n−1).

The first multiplication unit 222 multiplies the inputted n-th messagesymbol b_(k)(n) by the delay data d_(k)(n−1) inputted from the delayunit 224 and outputs the multiplication result d_(k)(n) to the delayunit 224 and the second multiplication unit 226.

Note that as discussed later as the performance evaluation of thecommunication system 1, the weight adjustment (training) of the filterunit 4 is performed using known data (pilot) preliminarily stored in thetransmitting device 2 and the filter unit 4, the above described process(differential encoding) by the delay unit 224 and the firstmultiplication unit 222 is not required.

In this case, the transmitting device 2 outputs the message symbolb_(k)(n) itself to the multiplication unit 226 as the multiplicationresult d_(k)(n).

The hopping pattern receiving unit 240 receives a hopping pattern P_(k)used for spread spectrum of the message symbol b_(k)(n) by frequencyhopping (FH) from the receiving device 3 via the antenna 210, the RF208, the A/D 212, and the receiving program 30 (described later byreferring to FIGS. 6 to 8) executed by the transmitting device 2-k, andoutputs it to the hopping pattern receiving unit 240.

The hopping pattern P_(k) can be expressed in an M×L matrix as shown inthe following expression 1, where the column component includes thenumber of components corresponding to the code length L (an L number ofcomponents of the time domain; L denotes an integer of 2 or more) perchip and the row component includes the M number (M denotes an integerof 2 or more) of elements of the frequency domain contained in asignature wave signal c_(k)(t) generated by the frequency synthesizerunit 244.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack & \; \\{P_{k} = \begin{bmatrix}p_{k,1,1} & p_{k,1,2} & \ldots & p_{k,1,M} \\p_{k,2,1} & p_{k,2,2} & \ldots & p_{k,2,M} \\\vdots & \vdots & \ddots & \vdots \\p_{k,L,1} & p_{k,L,2} & \ldots & p_{k,L,M}\end{bmatrix}} & (1)\end{matrix}$

The hopping pattern setting unit 242 replaces an old hopping patternP_(k) which has been used so far with a new hopping pattern P_(k)inputted from the hopping pattern receiving unit 240 to update thehopping pattern.

In addition, the hopping pattern setting unit 242 outputs the updatedhopping pattern P_(k) to the frequency synthesizer unit 244.

The frequency synthesizer unit 244 generates a signature wave signalc_(k)(t) of a frequency based on the hopping pattern P_(k) inputted fromthe hopping pattern setting unit 242 and outputs the signal to thesecond multiplication unit 226.

The second multiplication unit 226 operates as a quadrature modulator,performs complex multiplication on the multiplication result b_(k)(n)inputted from the first multiplication unit 222 and the signature wavesignal c_(k)(t) for spreading spectrum and outputs the signal to the D/A206 (FIG. 3) as digital data indicating the transmission signals_(k)(t).

The D/A 206 converts the digital data indicating the transmission signals_(k)(t) to an analog transmission signal s_(k)(t), which is convertedto a frequency used for transmission between the transmitting device 2and the receiving device 3 by the RF 208. Then, the frequency undergoespower amplification before being transmitted to each communication partythrough the antenna 210.

FIG. 6 illustrates a configuration of a receiving program 30 executed bythe transmitting device 2-k and the receiving device 3-k illustrated inFIG. 1.

FIG. 7 illustrates a configuration of a filter unit 4 of the receivingprogram 30 illustrated in FIG. 6.

FIG. 8 illustrates a configuration of the coefficient multiplicationunit 44 illustrated in FIG. 7.

As illustrated in FIG. 6, the receiving program 30 includes a timingcontrol unit 300, a filter unit 4, a decoding unit 32, and an updatingunit 34.

The decoding unit 32 includes an addition unit (Σ) 320, a demodulationunit 322, a delay unit 324, and a multiplication unit 326.

The updating unit 34 includes a received signal matrix (R_(k)(n))generation unit 340, a weight (W_(k)) updating unit 342, a hoppingpattern (P_(k)) generation unit 344, and a hopping pattern (P_(k))transmission unit 346.

As illustrated in FIG. 7, the filter unit 4 illustrated in FIG. 7includes an M number of function generation units 400-1 to 400-M eachcorresponding to an element of the frequency domain of the hoppingpattern P_(k); multiplication units 402-1 to 402-M, low pass filter(LPF) units 404-1 to 404-M, selection units 406-1 to 406-M, and 414, aselection control unit 408, a coefficient setting unit 410, a weightingunit 420 including a hopping pattern corresponding portion 422containing an M×L number of elements each corresponding to a hoppingpattern P_(k), and a total sum calculation unit (Σ) 412, whichconstitute an FIR filter.

Note that in the following description, for the purpose of clarifyingthe description, the reference numeral or reference character may befollowed by ( ) such as (1, 1), and thus the reference numeral orreference character may be different between the following descriptionand the corresponding drawing.

The weighting unit 420 includes an M×(L+α) number of delay units 424-(1,1) to 424-(M, L) and 424-(1, L+1) to 424-(M, L+α), an M×(L+α) number ofcoefficient multiplication units 44-(1, 1) to 44-(M, L) and 44-(1, L+1)to 44-(M, L+α), and an M×(L+α−1) number of addition units 428-(1, 1) to428-(M, L) to 428-(1, L+1) to 428-(M, L+α−1).

Of the components of the above weighting unit 420, the hopping patterncorresponding portion 422 corresponds to each of the M×L number of delayunits 424-(1, 1) to 424-(M, L), coefficient multiplication units 426-(1,1) to 426-(M, L), and addition units 428-(1, 1) to 428-(M, L).

It should be noted that apparently the technical scope of the presentinvention also covers the communication system 1 including a modifiedreceiving program 30 which further increases each component of theweighting unit 420 such that the M×(L+α) number of delay units 424,coefficient multiplication units 44 or the M×(L+α−1) number of additionunits are increased to the (M+1)×(L+α) number or the (M+1)×(L+α−1)number thereof, or further increase the number of each component of theweighting unit 420.

As illustrated in FIG. 8, the coefficient multiplication unit 44-m, lillustrated in FIG. 7 includes a register unit 440-m, l, amultiplication unit 442-m, l, and a coefficient storage unit 444-m, l.

Note that the delay units 424-m, l to (m, L+α) and the register units440-m, 1 to (m, L+α) illustrated in FIG. 7 serve as L+α stages of shiftregisters which shift complex data received from the previous stage tothe following stage every T_(c).

The receiving program 30 executed by the receiving device 3-k uses theabove components to receive a transmission signal from the transmittingdevices 2-1 to 2-K via the antenna 210, the RF 208, and the A/D 212(FIG. 3), and decodes a message symbol b′_(k)(n) from thedigital-converted transmission signal s′_(k)(t) to output the messagesymbol to the network or the like.

In addition, the receiving program 30 updates the weight matrix (W_(k))expressed in an M×(L+α) matrix used by the filter unit 4 by repeatingthe update a predetermined number of times so as to decode the messagesymbol b′_(k)(n) corresponding to the message symbol b_(k)(n) in thetransmitting device 2-k belonging to the same pairs with excellentperformance from the transmission signal s′_(k)(t) received from thetransmitting devices 2-1 to 2-K.

Of the updated weight matrices W_(k), the receiving program 30 transmits(feeds back) the element corresponding to the hopping patterncorresponding portion 422 to the transmitting device 2-k via the D/A206, the RF 208 and the antenna 210 as illustrated in FIG. 2 so as toupdate the hopping pattern P_(k).

That is, the hopping pattern P_(k) is defined as complex conjugatesw_(k, m, l) of numbers w*_(k, m, l) multiplied by a (first to M-throw)×(first to L-th column) of elements starting with the elementinputted to the filter unit 4 early in the weight matrices W_(k) (*preceded by a symbol denotes a complex conjugate number indicated by thesymbol).

It should be noted that the technical scope of the present inventionalso covers the communication system 1 including a modified receivingprogram 30 which associates the hopping pattern P_(k) with an element ofa weight matrix W_(k) different from the above in the time axisdirection.

As illustrated in FIGS. 6 to 8, in the receiving program 30 executed bythe receiving device 3-k, the timing control unit 300 controls thetiming of the operation of each component of the receiving program 30 soas to be synchronized with the message symbol b_(k)(n) and the chipillustrated in FIG. 5.

The selection control unit 408 controls the timing of the selection ofeach of the selection units 406 and 414.

The digital message symbol r(t) is inputted to the multiplication units402-1 to 402-M of the filter unit 4 of the receiving program 30.

Each function generation unit 400-m generates a function e^(−j2πζmt),and outputs the function to the multiplication unit 402-m.

Note that in the function e^(−j2πζmt), j is (−1)^(1/2), and ζ_(m)(Hz)denotes a frequency of the m-th tone of the spectrum spread transmissionsignal such as ζ_(m)=(m−1)/T_(c)(Hz).

Each multiplication unit 402-m operates as a quadrature modulator andperforms complex multiplication on the transmission signal r(t) inputtedfrom the A/D 212 (FIG. 3) and the function e^(−j2πζmt) inputted from thefunction generation unit 400-m to output the complex multiplicationresult r(t)e^(−j2πζmt) to the LPF 404-m.

Each LPF 404-m is implemented, for example, by an integrator whichintegrates the multiplication result r(t) e^(−j2πζmt) inputted from themultiplication unit 402-i from the time nT_(s)+(l−1)T_(c)+τ_(k, k, 1) tothe time nT_(s)+lT_(c)+τ_(k, k, 1).

In this case, each LPF 404-m passes the frequency component r_(k, m, l)(n) of an m-th tone of an 1-th chip for the purpose of decoding an n-thmessage symbol b_(k)(n) and outputs frequency component to the selectionunit 406-m.

In a timing (t=T_(s)+lT_(c)+τ_(k, k, 1)) when each LPF unit 404-mcompletes integration, the selection unit 406-m, according to thecontrol of the selection control unit 408, selects the frequencycomponent r_(k, m, l) (n) inputted from the LPF 404-m and outputs thefrequency component to the delay unit 424-m, 1 and the received signalmatrix generation unit 340.

When the frequency component r_(k, m, L+α)(n) of an m-th tone isinputted from each selection unit 406-m, the delay unit 424-(m, L+α)continuously outputs the frequency component r_(k, m, L+α)(n) of an(L+α−1) th chip giving a delay of T_(c) to each register 440-m, L+α andstores the frequency component therein.

Note that likewise, other delay units 424 also continuously each outputthe frequency component r_(k, m, l) to the corresponding register 440.The operation of the filter unit 4 is stabilized by continuouslyoutputting a value to each register 440 during the time period of T_(c).

Moreover, each delay unit 424-(m, L+α) sequentially gives a delay ofT_(c) to the frequency component r_(k, m, L+α)(n) inputted from eachselection unit 406-m at a cycle of T_(c) and outputs the result to eachdelay unit 424-(m, L+α−1) at the following stage.

When each of the (L+α−1) to second frequency componentr_(k, m, L+α−1)(n) to r_(k, m, 2)(n) is inputted from each of the delayunits 424-(m, L+α) to 424-(m, 3) at the previous stage, each of thedelay units 424-(m, L+α−1) to 424-(m, 2) outputs the (L+α−2) to firstfrequency component r_(k, m, L+α−2)(n) to r_(k, m, 1)(n) giving a delayof T_(c) at the previous stage to the register 440-m, l and stores ittherein.

In addition, each of the delay units 424-(m, L+α−1) to 424-(m, 2)sequentially gives a delay of T_(c) to the (L+α) to third frequencycomponent r_(k, m, L+α)(n) to r_(k, m, 3)(n) inputted from each of thedelay units 424-(m, L+α) to 424-(m, 3) at the previous stage at a cycleof T_(c) and outputs the result to each of the delay units 424-(m,L+α−2) to 424-(m, 1) at the following stage.

When each second frequency component r_(k, m, 2)(n) is inputted fromeach delay unit 424-(m, 2) at the previous stage, each delay unit424-(m, 1) outputs the first frequency component r_(k, m, 1)(n) giving adelay of T_(c) at the previous stage to each register 440-m, 1 andstores the frequency component therein.

Each register 440-m, l holds the frequency component r_(k, m, 1)(n)inputted from the delay unit 424-m, l and outputs the frequencycomponent to each multiplication unit 442-m, l.

Each coefficient storage unit 444-m, l holds each element m, l (weightw_(k, m, l)) of the weight matrix (W_(k)) set by the weight updatingunit 342 (FIG. 6) and outputs the element to each multiplication unit442-m, l.

Each multiplication unit 442-(m, L+α) performs complex multiplication oneach of the frequency components r_(k, m, L+α)(n) inputted from theregisters 440-(m, L+α), the weight w_(k, m, L+α), and the complexconjugate number w*_(k, m, L+α) and outputs the multiplication resultsto each addition unit 428-(m, L+α−1).

Each of the multiplication units 442-(m, L+α−1) to 442-(m, 1) performscomplex multiplication on each of the frequency componentsr_(k, m, L+α)(n) to r_(k, m, 1)(n), the weights w_(k, m, L+α) tow_(k, m, 2), and the complex conjugate numbers w*_(k, m, L+α) toW*_(k, m, l) and outputs the multiplication results to the respectiveaddition units 428-(m, L+α−1) to 424-(m, 1).

Each of the addition units 428-(m, L+α−1) to 428-(m, 2) performs complexaddition on the multiplication results inputted from the respectivemultiplication units 442-(m, L+α−1) to 442-(m, 2) and the additionresults inputted from the respective addition units 428-(m, L+α) to (m,3), and outputs the addition results to the respective addition units428-(m, L+α−2) to 428-(m, 1).

The addition unit 428-(m, 1) performs complex addition on themultiplication results inputted from the multiplication unit 442-(m, 1)and the addition results inputted from the addition unit 428-(m, 2) andoutputs the addition results to the total sum calculation unit 412.

The total sum calculation unit 412 calculates the total sum of theaddition results inputted from the addition unit 428-(m, 1) and outputsthe complex filter output data d′_(k)(n) to the selection unit 414.

The selection unit 414 selects the filter output data d′_(k)(n)calculated by the total sum calculation unit 412, and outputs the datato the demodulation unit 322 (FIG. 6).

The received signal matrix generation unit 340 generates an (L+α)×M ofreceived signal matrices R_(k)(n) from all frequency components fordecoding an n-th symbol outputted from each LPF 404-m, namely, thefrequency components r_(k, m, 1)(n) to r_(k, m, L)(n) and a part of thefrequency components r_(k, m, l)(n+1) (in the case of L>α, the frequencycomponents r_(k, m, 1)(n+1) to r_(k, m, α)(n+1) is also written as thefrequency components r_(k, m, L+1)(n) to r_(k, m, L+α)(n)), and outputsreceived signal matrices R_(k)(n) to the weight updating unit 342.

The weight updating unit 342 processes the received signal matrixR_(k)(n) inputted from the received signal matrix generation unit 340,for example, using an N-LMS (normalized least mean square) algorithm.

The weight updating unit 342 uses the above processing results and theerror data e_(k)(n) inputted from the addition unit 320 to optimize theweight w_(k, m, 1) contained in the weight matrix (W_(k)) so as todecode the message symbol b_(k)(n) from the transmission signal r_(k)(t)received from the transmitting device 2-k with better performance.

The hopping pattern generation unit 344 extracts a portion correspondingto the hopping pattern corresponding portion 422 from the weightw_(k, m, l) updated by the weight updating unit 342 to generate ahopping pattern P_(k) containing the weight w_(k, m, 1) to w_(k, m, L)and outputs the pattern to the hopping pattern transmission unit 346.

The hopping pattern transmission unit 346 outputs the message symbolb_(k)(n) indicating the hopping pattern P_(k) inputted from the hoppingpattern generation unit 344 to the transmitting program 22 (FIG. 4)executed by the receiving device 3-k so as to be transmitted to thetransmitting device 2-k via the A/D 212, the RF 208 and the antenna 210.

The demodulation unit 322 performs a process using a signum function(sgn(x); also called a code function) on the filter output datad′_(k)(n) received from the filter unit 4 to obtain the complexreference data d″_(k) as the processing result, and outputs thereference data to the delay unit 324 and the multiplication unit 326.

Note that the signum function sgn(x) is defined such that if x ispositive (x>0), +1 is returned; if x is negative (x<0), −1 is returned;and if x=0, 0, +1 or −1 is appropriately returned;

Note that generally x is unlikely to be 0 due to noise, there nopractical need to define the value returned by the signum function inthe case of x=0.

The delay unit 324 delays, by T_(s), the reference data d″_(k)(n)outputted from the demodulation unit 322 and outputs the reference datato the multiplication unit 326.

Note that as discussed later as the performance evaluation of thecommunication system 1, the weight adjustment (training) of the filterunit 4 is performed using known data (pilot) preliminarily stored in thetransmitting device 2 and the filter unit 4, the above described process(differential decoding) by the above described demodulation unit 322 andthe delay unit 324 is not required.

In this case, in the receiving device 3, the reference data d″_(k)(n) isassumed to be the demodulated message symbol b_(k)(n).

The multiplication unit 326 multiplies the reference data d″_(k)(n)inputted from the demodulation unit 322 and the reference datad″_(k)(n−1) delayed by the delay unit 324 to decode the message symbolb_(k)(n) and outputs the message symbol b_(k)(n) to a network or thelike connected to the receiving device 3-k.

The addition unit 320 subtracts the filter output data d′_(k)(n)outputted from the processing result data filter unit 4 from thereference data d″_(k)(n) outputted from the demodulation unit 322 togenerate the error data e_(k)(n) and outputs the error data e_(k)(n) tothe weight updating unit 342.

[Communication Between Transmitting Device 2-k and Receiving Device 3-k]

Hereinafter, the communication between the transmitting device 2-k andthe receiving device 3-k which transmit the message symbol b_(k)(n) toeach other as a pair of communication devices in the communicationsystem 1 (FIG. 1) will be described.

[Transmitting Device 2-k]

First, the process in the transmitting device 2-k will be described.

In the transmitting device 2-k, the multiplication unit 222 of thetransmitting program 22 (FIG. 4) receives the message symbol b_(k)(n)from the network or the like.

The multiplication unit 222 and the delay unit 224 processes theinputted message symbol b_(k)(n) to generate a differentially encodedcomplex symbol d_(k)(n) and outputs the symbol d_(k)(n) to the delayunit 224.

The differentially encoded complex symbol d_(k)(n) is defined asd_(k)(n)=b_(k)(n) d_(k)(n−1) using an n-th inputted message symbolb_(k)(n) and an (n−1)-th generated differentially encoded complex symbold_(k)(n−1).

Meanwhile, the hopping pattern setting unit 242 sets an initial value ofthe hopping pattern P_(k) or the hopping pattern P_(k) updated by thereceiving device 3-k of the communication party and received by thehopping pattern receiving unit 240, to the frequency synthesizer unit244.

The frequency synthesizer unit 244 uses the set hopping pattern P_(k) togenerate a signature waveform signal c_(k)(t) defined in the followingexpression 2 and outputs the signal c_(k)(t) to the multiplication unit226.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 2} \right\rbrack & \; \\{{c_{k}(t)} = {\sum\limits_{l = 1}^{L}\;{a_{k,l}\left( {t - {\left( {l - 1} \right)T_{c}}} \right)}}} & (2)\end{matrix}$

In the expression 2, T_(c) denotes the time length of the chipillustrated in FIG. 5 and defined as T_(c)>t>0; and α_(k, 1)(t) definesan 1-th chip waveform defined as the following expression 3.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 3} \right\rbrack & \; \\{{a_{k,l}(t)} = {{g(t)}{\sum\limits_{m = 1}^{M}\;{p_{k,l,m}{\mathbb{e}}^{{j2\pi}\;\xi\;{mt}}}}}} & (3)\end{matrix}$

In the expression 3, the rectangular function g(t) is defined as thefollowing expression 4.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 4} \right\rbrack & \; \\{{g(t)} = \left\{ \begin{matrix}1 & \left( {0 < t < T_{c}} \right) \\0 & ({otherwise})\end{matrix} \right.} & (4)\end{matrix}$

Meanwhile, as described above, the frequency hopping pattern P_(k) usedto spread spectrum of the message symbol b_(k)(n) in the transmittingdevice 2-k can be defined as an M×L matrix shown in the followingexpression 5.

Note that in the expression 5, L denotes the number of chips containedin one message symbol illustrated in FIG. 5; and M denotes the number oftones used for frequency hopping.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 5} \right\rbrack & \; \\{P_{k} = \begin{bmatrix}p_{k,1,1} & p_{k,1,2} & \ldots & p_{k,1,M} \\p_{k,2,1} & p_{k,2,2} & \ldots & p_{k,2,M} \\\vdots & \vdots & \ddots & \vdots \\p_{k,L,1} & P_{k,L,2} & \ldots & p_{k,L,M}\end{bmatrix}} & (5)\end{matrix}$

The multiplication unit 226 multiplies the signature waveform signalc_(k)(t) inputted from the hopping pattern setting unit 242 and thedifferentially encoded complex symbol d_(k)(n) inputted from themultiplication unit 222 to generate the transmission signal s_(k)(t)defined in the following expression 6 as the multiplication result andoutputs the transmission signal s_(k)(t) to the D/A 206.

The D/A 206, the RF 208, and the antenna 210 (FIG. 3) transmit theinputted transmission signal s_(k)(t) to the receiving device 3-k of thecommunication party.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 6} \right\rbrack & \; \\{{s_{k}(t)} = {\sum\limits_{n = 0}^{\infty}\;{{d_{k}(n)}{c_{k}\left( {t - {nT}_{s}} \right)}}}} & (6)\end{matrix}$

Note that in the expression 6, T_(s) denotes the code time length of themessage symbol b_(k)(n) illustrated in FIG. 5 and defined asLT_(s)=T_(c).

Moreover, the expression 6 indicates differentially encoded complexsymbol d_(k)(n)=b_(k)(n)·d_(k)(n−1) and a differentially encoded complexsymbol transmitted during nT_(s)>t>(n−1)T_(s).

As described above, the message symbol b_(k)(n) is generated, forexample, assuming that a QPSK modulation system is used.

[Transmission Channel Between Transmitting Device 2-k and ReceivingDevice 3-k]

Next, a non-target signal received by the transmitting device 2-killustrated FIG. 1 and the like will be described.

In the communication system 1, a transmission signal is transmittedindependently to each pair of communication devices.

In this case, the receiving device 3-k receives transmission signalsfrom the transmitting devices 2-1 to 2-(k−1), 2-(k+1) to 2-K asillustrated in FIG. 2.

In other words, the receiving device 3-k receives not only atransmission signal from the receiving device 3-k of the communicationparty but also unwanted signals and noise from the transmitting devices2-k′ of other pairs.

Note that in FIG. 2, h_(k′, k)(t) denotes a complex impulse responsefunction which the path from the transmitting device 2-k′ to thereceiving device 3-k gives to a transmission signal from thetransmitting device 2-k′ to the receiving device 3-k, and is defined inthe following expression 7.

In addition, in FIG. 2, AWGN denotes additive white Gaussian noise whichthe receiving device 3-k receives together with the transmissionsignals.

Note that in the expression 7, h_(k′, i) denotes a complex gain constantdefined in an i-th transmission channel; and τ_(k′, k, i)(Tc>τ_(k′, k, i)>0) denotes a delay defined in an i-th transmissionchannel.

In addition, in the expression 7, h_(k′, k) denotes the number of pathscontained in the path from the transmitting device 2-k to the receivingdevice 3-k.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 7} \right\rbrack & \; & \; \\{{h_{k^{\prime},k}(t)} = {\sum\limits_{i = 1}^{I_{k^{\prime},k}}\;{h_{k^{\prime},k,i}{\delta\left( {t - T_{k^{\prime},k,i}} \right)}}}} & \; & (7)\end{matrix}$

The transmission signal r_(k)(t) received by the receiving device 3-k isformulated by the following expressions 8-1 and 8-2.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 8} \right\rbrack & \; \\\begin{matrix}{{r_{k}(t)} = {{\sum\limits_{k^{\prime} = 1}^{K}\;\left( {{s_{k^{\prime}}(t)}*{h_{k^{\prime},k}(t)}} \right)} + {n(t)}}} \\{= {{\sum\limits_{k^{\prime} = 1}^{K}\;{\sum\limits_{n = 0}^{\infty}\;{\sum\limits_{i = 1}^{I_{k^{\prime},k}}\;{h_{k^{\prime},k,i}{d_{k}(n)}{c_{k}\left( {t - {nTs} - T_{k^{\prime},k,i}} \right)}}}}} + {n(t)}}}\end{matrix} & \begin{matrix}\left( {8\text{-}1} \right) \\\left( {8\text{-}2} \right)\end{matrix}\end{matrix}$[Receiving Device 3-k]

Next, the process in the receiving device 3-k will be described.

In the receiving device 3-k, the RF 208 (FIG. 3) receives a transmissionsignal r_(k)(t) shown in the expressions 8-1 and 8-2 via the antenna210, converts the transmission signal to a transmission signal s_(k)(t)of a baseband or an intermediate frequency which can be processed by theDSP 202 and the like, and outputs the transmission signal s_(k)(t) tothe A/D 212.

The A/D 212 converts the transmission signal r_(k)(t) inputted from theRF 208 to a digital transmission signal r_(k)(t) and outputs thetransmission signal r_(k)(t) to the DSP 202 and the like.

The receiving program 30 (FIGS. 6 to 8) is executed in the DSP 202 andthe like in the receiving device 3-k.

In the filter unit 4 of the receiving program 30, the multiplicationunit 402-m multiplies the inputted transmission signal r_(k)(t) by afunction e^(−j2πηmt) and outputs the multiplication resultr(t)e^(−j2πηmt) to the LPF 404-m.

Each LPF 404-m sequentially integrates the multiplication resultr(t)e^(−j2πζmt) during nT_(s)+(l−1)T_(c)+τ_(k′, k, i) tonT_(s)+lT_(c)+τ_(k′, k, i) as shown in the following expressions 9-1 and9-2, and outputs the result to the weighting unit 420.

As a result of integration by the LPF 404-m, as shown in the followingexpressions 9-1 and 9-2, an m-th tone of component contained in thetransmission signal r_(k)(t) is separated individually.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 9} \right\rbrack & \; \\\begin{matrix}{{r_{k,l,m}(n)} = {\int_{{nT}_{s} + {{({l - 1})}T_{c}} + \tau_{k,k,1}}^{{nT}_{s} + {lT}_{c} + \tau_{k,k,1}}{{r_{k}(t)}{\mathbb{e}}^{{- {j2\pi}}\;\xi\;{mt}}\ {\mathbb{d}t}}}} \\{= {\int_{{{nT}_{s} + {{({l - 1})}T_{c}} + {\tau k}},k,1}^{{nT}_{s} + {lT}_{c} + \tau_{k,k,1}}{{r_{k}(t)}{\mathbb{e}}^{{- j}\frac{2{\pi{({m - 1})}}}{Tc}t}\ {\mathbb{d}t}}}}\end{matrix} & \begin{matrix}\left( {9\text{-}1} \right) \\\left( {9\text{-}2} \right)\end{matrix}\end{matrix}$

Note that as described above, the expressions 9-1 and 9-2 assumeL+α≧l≧1, ζ_(m)(Hz) denotes an m-th tone frequency in the spectrum spreadtransmission signal, and is defined as ζ_(m)=(m−1)/T_(c)(Hz).

The received signal matrix generation unit 340 generates a receivedsignal matrix R_(k)(n) defined in the following expression 10 from thefrequency component r_(k, m, 1)(n), r_(k, 1)(n+1) obtained in the timelength t (nT_(s)+(L+α)T_(c)+τ_(k′, k, i)>t>nT_(s)+τ_(k′, k, i)).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 10} \right\rbrack & \; \\{{R_{k}(n)} = \begin{bmatrix}{r_{k,1,1}(n)} & {r_{k,1,2}(n)} & \ldots & {r_{k,1,M}(n)} \\{r_{k,2,1}(n)} & {r_{k,2,2}(n)} & \ldots & {r_{k,2,M}(n)} \\\vdots & \vdots & \ddots & \vdots \\{r_{k,L,1}(n)} & {r_{k,L,2}(n)} & \ldots & {r_{k,L,M}(n)} \\{r_{k,1,1}\left( {n + 1} \right)} & {r_{k,1,2}\left( {n + 1} \right)} & \ldots & {r_{k,1,M}\left( {n + 1} \right)} \\{r_{k,2,1}\left( {n + 1} \right)} & {r_{k,2,2}\left( {n + 1} \right)} & \ldots & {r_{k,2,M}\left( {n + 1} \right)} \\\vdots & \vdots & \ddots & \vdots \\{r_{k,\alpha,1}\left( {n + 1} \right)} & {r_{k,\alpha,2}\left( {n + 1} \right)} & \ldots & {r_{k,\alpha,M}\left( {n + 1} \right)}\end{bmatrix}} & (10)\end{matrix}$

Meanwhile, the filter output data d′_(k)(n) outputted from the filterunit 4 is defined in the following expression 11.

Note that in the expression 11, H denotes a complex conjugate and atransposition of the matrix; and tr denotes a trace of the matrix.[Expression 11]d′k(n)=tr└w _(k) ^(H)(n)R _(k)(n)┘  (11)

The demodulation unit 322 performs a process using a signum function onthe filter output data d′_(k)(n) as shown in the following expression 12to generate reference data d″_(k)(n).

Note that in the expression 12, sgn denotes a signum function, Re[x]denotes a real number component of a complex number x, and Im[x] denotesa imaginary number component of the complex number x.[Expression 12]d″k(n)=sgn[Re[{circumflex over (d)}_(k)(n)]]+j sgn[Im[{circumflex over(d)} _(k)(n)]]  (12)

The multiplication unit 326 performs complex multiplication on an n-threference data d″_(k)(n) and an (n−1)-th reference data d″_(k)(n) asshown in the following expressions 13-1 to 13-3 to obtain the messagesymbol b′_(k)(n).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 13} \right\rbrack & \; \\\begin{matrix}{{{\overset{\sim}{b}}_{k}(n)} = {d^{''}{k(n)}d^{''}k*\left( {n - 1} \right)}} \\{= {\left( {{{sgn}\left\lbrack {{Re}\left\lbrack {{\hat{d}}_{k}(n)} \right\rbrack} \right\rbrack} + {{jsgn}\left\lbrack {{Im}\left\lbrack {{\hat{d}}_{k}(n)} \right\rbrack} \right\rbrack}} \right) \times}} \\{\left( {{{sgn}\left\lbrack {{Re}\left\lbrack {{\hat{d}}_{k}\left( {n - 1} \right)} \right\rbrack} \right\rbrack} + {{jsgn}\left\lbrack {{Im}\left\lbrack {{\hat{d}}_{k}\left( {n - 1} \right)} \right\rbrack} \right\rbrack}} \right)}\end{matrix} & \begin{matrix}\left( {13\text{-}1} \right) \\\left( {13\text{-}2} \right) \\\left( {13\text{-}3} \right)\end{matrix}\end{matrix}$

The addition unit 320 subtracts the filter output data d′_(k)(n)outputted from the filter unit 4 from the reference data d″_(k)(n)outputted from the demodulation unit 322 to generate the error datae_(k)(n) defined in the following expression 14 and outputs the errordata e_(k)(n) to the weight updating unit 342.

As will be apparent from the generation method, the error data e_(k)(n)indicates the difference between the reference data d″_(k)(n) and thefilter output data d′_(k). The weight updating unit 342 updates andoptimizes the weight so as to minimize the value of the error datae_(k)(n), namely, so that the value of the reference data d″_(k)(n)comes close to the value of the filter output data d′_(k).[Expression 14]e _(k)(n)={tilde over (d)}_(k)(n)−tr└w _(k) ^(H)(n)R _(k)(n)┘  (14)

The weight updating unit 342 is defined in the following expression 15;uses the received signal matrix R_(k)(n) and the error data e_(k)(n) toupdate the weight matrix W_(k)(n) used by the filter unit 4 to processan n-th message symbol b_(k)(n) as shown in the following expression 16;generates a weight matrix W_(k)(n+1) used to process an (n+1) th orlater message symbol b_(k); and outputs the weight matrix to thecoefficient setting unit 410 of the filter unit 4 and hopping patterngeneration unit 344.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 15} \right\rbrack & \; \\{W_{k} = \begin{bmatrix}w_{k,1,1} & w_{k,1,2} & \ldots & w_{k,1,M} \\w_{k,2,1} & w_{k,2,2} & \ldots & w_{k,2,M} \\\vdots & \vdots & \ddots & \vdots \\w_{k,L,1} & w_{k,L,2} & \ldots & w_{k,L,M} \\w_{k,{L + 1},1} & w_{k,{L + 1},2} & \ldots & w_{k,{L + 1},M} \\w_{k,{L + 2},1} & w_{k,{L + 2},2} & \ldots & w_{k,{L + 2},M} \\\vdots & \vdots & \ddots & \vdots \\w_{k,{L + \alpha},1} & w_{k,{L + \alpha},2} & \ldots & w_{k,{L + \alpha},M}\end{bmatrix}} & (15)\end{matrix}$

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 16} \right\rbrack & \; \\{{W_{k}\left( {n + 1} \right)} = {{W_{k}(n)} + {\frac{\mu}{{{R_{k}(n)}}_{F}^{2}}{R_{k}(n)}{{\mathbb{e}}_{k}^{*}(n)}}}} & (16)\end{matrix}$

Note that ∥R_(k)(n)∥_(F) in the expression 15 denotes a Frobenius normof the received signal matrix R_(k)(n) defined in the followingexpression 17.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 17} \right\rbrack & \; \\{{{R_{k}(n)}}_{F} = \sqrt{\sum\limits_{l = 1}^{L + \alpha}\;{\sum\limits_{m = 1}^{M}\;{{r_{k,l,m}(n)}}^{2}}}} & (17)\end{matrix}$

Each time the weight updating unit 342 updates the weight matrixW_(k)(n+1), the coefficient setting unit 410 sets the element m,l(weight w_(k, m, 1)(n)) of a new weight matrix W_(k)(n+1) to eachcoefficient storage unit 444-m, l of the coefficient multiplicationunits 44-(m, 1), for example, at the boundary of a message symbolinputted to the filter unit 4.

Note that as the initial value of the weight matrix W_(k), for example,the weight matrix W_(k)(0) defined in the following expression 18 isused.

Note that in the expression 18, T denotes a transposition of the matrixand 0_(α×M)T denotes a zero matrix with a size of α×M.[Expression 18]W _(k)(0)=└P _(k) ^(T)(0)O _(α×M) ^(T)┘^(T)  (18)

The filter unit 4 uses the weight matrix W_(k)(n+1) updated as describedabove to perform filtering on the next (n+1) th transmission signalr_(k)(t). The decoding unit 32 processes the filter output datad′_(k)(n+1) outputted from the filter unit 4 to decode the messagesymbol b′_(k)(n) corresponding to the message symbol b_(k)(n) processedby the transmitting program 22 executed in the transmitting device 2-k.

[Feedback of Hopping Pattern P_(k)]

Hereinafter, the feedback process of the hopping pattern P_(k) from thereceiving device 3-k to the transmitting device 2-k will be described.

The hopping pattern generation unit 344 of the receiving program 30executed in the receiving device 3-k extracts a part of the weightmatrix W_(k) inputted from the weight updating unit 342 corresponding tothe hopping pattern corresponding portion 422 (FIG. 7) as shown in theexpressions 19-1 and 19-2 to generate an new hopping pattern P_(k)(λ)and outputs the hopping pattern P_(k)(λ) to the hopping patterntransmission unit 346.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 19} \right\rbrack & \; \\\begin{matrix}{{P_{k}(\lambda)}\left( {\underset{=}{\Delta}\begin{matrix}p_{k,1,1} & p_{k,1,2} & \ldots & p_{k,1,M} \\p_{k,2,1} & p_{k,1,2} & \ldots & p_{k,2,M} \\\vdots & \vdots & \ddots & \vdots \\p_{k,L,1} & p_{k,L,2} & \ldots & p_{k,L,M}\end{matrix}} \right)} \\{= \begin{bmatrix}{w_{k,1,1}\left( {\hat{n}}_{k} \right)} & {w_{k,1,2}\left( {\hat{n}}_{k} \right)} & \ldots & {w_{k,1,M}\left( {\hat{n}}_{k} \right)} \\{w_{k,2,1}\left( {\hat{n}}_{k} \right)} & {w_{k,2,2}\left( {\hat{n}}_{k} \right)} & \ldots & {w_{k,2,M}\left( {\hat{n}}_{k} \right)} \\\vdots & \vdots & \ddots & \vdots \\{w_{k,L,1}\left( {\hat{n}}_{k} \right)} & {w_{k,L,2}\left( {\hat{n}}_{k} \right)} & \ldots & {w_{k,L,M}\left( {\hat{n}}_{k} \right)}\end{bmatrix}}\end{matrix} & \begin{matrix}\left( {19\text{-}1} \right) \\\left( {19\text{-}2} \right)\end{matrix}\end{matrix}$

Note that the expressions 19-1 and 19-2 exemplifies that the hoppingpattern P_(k)(λ) is fed back from the receiving device 3-k to thetransmitting device 2-k at the time t=λT_(f)+Δ_(k)+αT_(c)+τ_(k, k, 1).

In the expressions 19-1 and 19-2, λ is defined as N_(f)≧λ≧1; N_(f)denotes the number of times the feedback is repeated; T_(f) denotes atime interval of the feedback; Δ_(k)(T_(f)≧Δ_(k)≧0) denotes an offsettime preliminarily determined for feedback timing.

Note that in the expressions 19-1 and 19-2, a transmission delay fromthe receiving device 3-k to the transmitting device 2-k is ignored.

Moreover, in the expressions 19-1 and 19-2, the symbol shown in thefollowing expression 20 is defined in the following expression 21.

In the expression 21, {q} denotes a maximum positive integer equal to orless than q.[Expression 20]{circumflex over (n)} _(k)  (20)[Expression 21]{circumflex over (n)} _(k) Δ {(λT _(f)+Δ_(k) +αT _(c)+τ_(k,k,1))/T_(s)}  (21)

The hopping pattern transmission unit 346 transmits the new hoppingpattern P_(k)(λ) inputted from the hopping pattern generation unit 344to the transmitting device 2-k via the A/D 212, the RF 208 and theantenna 210 (FIG. 3) as illustrated in FIG. 2.

In the transmitting program 22 executed in the transmitting device 2-k,the hopping pattern receiving unit 240 receives the hopping patternP_(k)(λ) from the receiving device 3-k and outputs the hopping patternP_(k)(λ) to the hopping pattern setting unit 242.

The hopping pattern setting unit 242 sets the hopping pattern P_(k)(λ)to the frequency synthesizer unit 244, which generates the signaturewave signal c_(k)(t) based on the hopping pattern P_(k)(λ) and performsspread spectrum on the message symbol b_(k)(n).

Note that the initial value P_(k)(0) of the hopping pattern P_(k) set bythe frequency synthesizer unit 244 is sequentially optimized by updatingthe hopping pattern P_(k) described above, and thus, for example, may bea value preliminarily determined by experiment or may be a random value.

In the above configured communication system 1, the data transmissionbetween the transmitting device 2-k and the receiving device 3-k canminimize the ISI (intersymbol interference) and the MAI (multiple accessinterference).

Moreover, the update of the hopping pattern P_(k) of the transmittingdevice 2-k allows the reference data d″_(k)(n) to achieve the MMSE(minimum mean-squared error) due to the update.

Therefore, according to the update of the hopping pattern P_(k)described above, data transmission with an extremely small bit errorrate (BER) can be provided between the transmitting device 2-k and thereceiving device 3-k.

[Overall Operation of Transmitting Device 2-k and Receiving Device 3-k]

Hereinafter, the overall operation of the data transmission between thetransmitting device 2-k and the receiving device 3-k, the feedback ofthe hopping pattern P_(k), and the update thereof will be described.

FIG. 9 illustrates a communication sequence diagram illustrating thedata transmission and the feedback (S10) of the hopping pattern P_(k)between the transmitting device 2-k and the receiving device 3-killustrated in FIG. 1 and the like.

In step 100-1 (S100-1), the transmitting device 2-k transmits atransmission signal s_(k)(t) to the receiving device 3-k a plurality ofnumber of times.

In step 102-1 (S102-1), the receiving device 3-k updates the weightmatrix W_(k) and the hopping pattern P_(k) at the time intervalsdescribed by referring to the expressions 19-1 and 19-2.

In step 104-1 (S104-1), the receiving device 3-k transmits or feeds backthe updated hopping pattern P_(k) to the transmitting device 2-k.

In step 106-1 (S106-1), the transmitting device 2-k updates the hoppingpattern P_(k) by replacing the previous hopping pattern P_(k) with thenew hopping pattern P_(k) received from the receiving device 3-k anduses the updated hopping pattern P_(k) for spread spectrum.

The above described process is repeated, for example, an N_(f) number oftimes between the transmitting device 2-k and the receiving device 3-k.

[Variation]

Hereinafter, a variation of the communication system 1 (FIG. 1, etc.)will be described.

The description has been made such that the feedback of the hoppingpattern P_(k) and the update thereof are repeated an N_(f) number oftimes between the transmitting device 2-k and the receiving device 3-k.However, for example, the number of times of the feedback and the updateis not limited but the feedback and the update may be performed at aconstant time interval or at random times.

Moreover, as illustrated by dotted lines in FIG. 6, the receivingprogram 30 may be configured such that a quality measurement unit 360which measures the signal intensity or the SN (signal noise) ratio ofthe transmission signal r_(k)(t) is added to the receiving program 30,and when the transmission signal quality becomes lower than a specifiedlevel, the updating unit 34 performs the feedback and the update of thehopping pattern P_(k) to improve the transmission signal quality.

Moreover, if the message symbol b_(k)(n) contains an error detectioncode, as illustrated by dotted lines in FIG. 6, the receiving program 30may be configured such that an error rate measurement unit 362 whichmeasures the error rate of the message symbol b′_(k)(n) obtained bydecoding is added to the receiving program 30, and when the error rateof the message data b′_(k)(n) reaches or exceeds a specified level, theupdating unit 34 performs the feedback and the update of the hoppingpattern P_(k) to reduce the error rate.

Moreover, the description has been made such that in the communicationsystem 1, the transmitting device 2 and the receiving device 3 usefrequency hopping to spread spectrum of the message symbol b_(k)(n).However, for example, the communication system 1 may be configured suchthat the transmitting device 2 and the receiving device 3 use a hoppingpattern made of two time domains or frequency components to perform theupdate and the feedback of the hopping pattern.

Moreover, the description has been made such that in the communicationsystem 1, the weight matrix W_(k) is optimized by the N-LMS algorithm toupdate the hopping pattern P_(k), but the update optimization algorithmmay be appropriately changed to another algorithm depending on theconfiguration and the application of the communication system 1 and theperformance of the DSP 202.

EMBODIMENTS

Hereinafter, an embodiment of the communication system according to thepresent invention will be specifically described by focusing how thecommunication system 1 can improve the transmission performance betweenthe transmitting device 2-k and the receiving device 3-k.

First, as the initial value of the hopping pattern P_(k), a hoppingpattern P_(k)(0) with L=7, M=8 using frequency hopping codes proposed inNon-Patent Document 3 and an M number of Gold sequences with a length ofL are used.

The frequency hopping code y_(k) of the hopping pattern P_(k)(0) isdefined in the following expressions 22-1 and 22-2.[Expression 22]y _(K) =x _(k)·β⊕γ_(k)·1  (22-1)=[y _(k,1) y _(k,2) . . . y _(k,L)]^(T)  (22-2)

In the expression 22, β=[β⁰, β¹, β², . . . , β^(L-1)]; β denotes aninitial element of GF (M=2³); x_(k), γ_(k) δ GF(2³); and l denotes acolumn vector with an 1 number of elements in all and having a length ofL.

In the expression 22, the symbol and “•” shown in the expression 23denote addition and multiplication with respect to GF(2³) respectively.[Expression 23]⊕  (23)

The value of x_(k), y_(k) with respect to a k-th signal is obtained by(k−1)=y_(k)+x_(k). The element v_(k, l, m) of (l, m) of an L×M matrixV_(k) is defined in the following expression 24.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 24} \right\rbrack & \; \\{v_{k,l,m} = \left\{ \begin{matrix}1 & \left( {m = {y_{k,l} + 1}} \right) \\0 & \left( {m \neq {y_{k,l} + 1}} \right)\end{matrix} \right.} & (24)\end{matrix}$

Here, when an M number of diagonal matrix sets Z₀, Z₁, . . . Z_(M-1)each containing an M number of Gold sequences on the diagonal linethereof are defined, the initial hopping pattern P_(k)(0) is defined asP_(k)(0)=Z_(xk)V_(k).

For example, if k=2, y₂, V₂, Z_(xk)=₂, P_(k)(0) is as shown in thefollowing expressions 25 to 27, 28-1, and 28-2.[Expression 25]y ₂=[1 2 4 3 6 7 5]^(T)  (25)

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 26} \right\rbrack & \; \\{v_{2} = \begin{bmatrix}0 & 1 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 1 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 \\0 & 0 & 0 & 1 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 1 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & 1 \\0 & 0 & 0 & 0 & 0 & 1 & 0 & 0\end{bmatrix}} & (26)\end{matrix}$

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 27} \right\rbrack & \; \\{Z_{{x2} = 1} = \begin{bmatrix} + & 0 & 0 & 0 & 0 & 0 & 0 \\0 & + & 0 & 0 & 0 & 0 & 0 \\0 & 0 & - & 0 & 0 & 0 & 0 \\0 & 0 & 0 & + & 0 & 0 & 0 \\0 & 0 & 0 & 0 & + & 0 & 0 \\0 & 0 & 0 & 0 & 0 & + & 0 \\0 & 0 & 0 & 0 & 0 & 0 & - \end{bmatrix}} & (27)\end{matrix}$

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 28} \right\rbrack & \; \\\begin{matrix}{{P_{2}(0)} = {Z_{{x2} = 1}V_{2}}} \\{= \begin{bmatrix}0 & + & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & + & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & - & 0 & 0 & 0 \\0 & 0 & 0 & + & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & + & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & + \\0 & 0 & 0 & 0 & 0 & - & 0 & 0\end{bmatrix}}\end{matrix} & \begin{matrix}\left( {28\text{-}1} \right) \\\left( {28\text{-}2} \right)\end{matrix}\end{matrix}$

FIG. 10 illustrates a model of a path for evaluating the performance ofthe communication system 1.

Further, in order to evaluate the performance of the communicationsystem 1, as illustrated in FIG. 10, a six-path model indicatingexponential decay performance is assumed (I_(k′, k)=6 for every k, k′).

As illustrated in FIG. 10, relative intensities |h_(k′, k, i)| are 20log₁₀|h_(k′, k, i+1)|/|h_(k′, k, i)|=−3 dB (where i=1, 2, . . . ,I_(k′, k)−1)).

The path delays τ_(k′, k, i) areτ_(k′, k, i+1)−τ_(k′, k, i)=(L+1)T_(c)/16 (for ≈T_(s)/16; L=7).τ_(k′, k, 1) for all k′, k and θ_(k, k, i+1) for all k′, k, i arestatistically independent of each other and are uniformly distributedrandom variables in the interval of [0,T) and [0,2π).

Note that for simplifying the assumption, as described above, theamplitude attenuation is assumed to be the same −3 dB for all k′, k, andτ_(k′, k, 1), θ_(k, k, i+1) is assumed to be independent for all k′, k,i, which provides a very strict path condition in the communicationsystem 1.

The communication system 1 requires an initial training period from whenthe transmitting device 2 feeds back a part of weight matrix (W_(k)) tothe receiving device 3 as the hopping pattern P_(k) to when thetransmitting device 2 is ready to generate an appropriate signaturewaveform signal c_(k)(t) according to the actual path condition.

The communication system 1 assumes that the initial training period ist<(N_(f)+1)T_(f)+Δ_(k)+τ_(k, k, 1) as described above.

The steady bit error rate (BER) in the communication system 1 shownbelow is obtained after the initial training period, and during thesteady period, the weight matrix W_(k) is updated only on the receivingdevice 3-k side, but the hopping pattern P_(k) is not fed back to thetransmitting device 2-k.

Moreover, the reference data d″_(k) used to update the weight matrixW_(k) is assumed to be d″_(k)=d_(k) during the initial training period,which means that a pilot data symbol used during the initial trainingperiod is stored in the transmitting device 2 and the stored pilot datasymbol is used during the initial training period.

The BER performance slightly depends on a randomly selected valueτ_(k′, k, 1), θ_(k, k, i+1), and thus points in the graphs in thefollowing drawings are each an average of the values obtained by fivesimulations.

The simulation conditions including the above assumptions are listed inthe following Table 1.

TABLE 1 SIMULATION CONDITIONS COMMUNICATION FCSS/ DS-CDMA SYSTEM 1DS-CDMA (MF, RAKE) Data QPSK E_(b)/N_(o) 9.9 dB L 7 31 α 0,7 0,31 — M 81 T_(f) 10⁴T_(s) — N_(f) 0,10 — Δ_(k) UNIFORMLY RANDOM — DISTRIBUTED IN[0,Tf) OPTIMIZATION N-LMS (μ = 0.1) — ALGORITHM[Performance Evaluation Results by Simulation]

Hereinafter, the results obtained by evaluating the performance of thecommunication system 1 by computer simulation will be described.

The computer simulation is used to compare the BER performance of thecommunication system 1 with the BER performance of a communicationsystem which adopts the DS-CDMA using a conventional Gold sequence, usesa matched filter, and uses or does not use a RAKE combining method, andthe BER performance of a communication system adopting the FCSS/CDMAsystem.

FIG. 11 is a graph of the BER performance with respect to the number ofactive transmission signals s_(k)(t) in the communication system 1.

FIG. 12 is a graph of the BER performance with respect to E_(b)/N_(o)for K=32.

FIGS. 13A to 13D each are a graph illustrating an initial hoppingpattern, the updated hopping pattern, and the corresponding powerspectra.

Note that in FIG. 13, the tone level p_(k, l, m) is indicated by theabsolute value |p_(k, l, m)|.

As will be understood from FIG. 11, in the communication systems eachadopting a conventional DS-CDMA system, as the number of activetransmission signals s_(k)(t) increases, the BER increases rapidly.

In contrast to this, in the communication system 1 with α=7 andN_(f)=10, as the number of active transmission signals s_(k)(t)increases, the error rate increases most gradually.

Moreover, as will be understood from FIG. 12, in comparison with thesystem adopting the FCSS/DS-CDMA (α=31 and N_(f)=10), in thecommunication system 1 (α=7 and N_(f)=10), a gain of 0.3 dB is obtainedwhen the BER is 10⁻³.

Moreover, as will be understood from FIG. 13C, the initial valueP_(k)(0) of the hopping pattern contains one tone for each chip, but theupdated hopping pattern contains a plurality of tones for each chip.

The above embodiments are provided for illustration and explanationpurposes, and do not cover all embodiments of the present invention.

Moreover, the above embodiments are not intended to limit the technicalscope of the present invention to the particular forms disclosed, andvarious modifications and variations can be made by referring to theparticular forms disclosed.

Further, the above embodiments are selected and described so as todescribe the principle and actual applications of the present inventionin the most appropriate manner. Therefore, based on the particular formsdisclosed in the above embodiments, those skilled in the art can use thepresent invention and the embodiments thereof by making variousmodifications to be suitable for every possible actual application.

Further, the technical scope of the present invention is intended to bedefined by the description and the equivalents.

DESCRIPTION OF SYMBOLS

1 communication system 2 transmitting device 200 IF 202 DSP 204, 216memory 206 D/A 208 RF 210 antenna 212 A/D 214 CPU 218 UI 22 transmittingprogram 220 timing control unit 222, 226 multiplication unit 224 delayunit 240 hopping pattern receiving unit 242 hopping pattern setting unit244 frequency synthesizer unit 3 receiving device 30 receiving program300 timing control unit 32 decoding unit 320 addition unit 322demodulation unit 324 delay unit 326 multiplication unit 34 updatingunit 340 received signal matrix generation unit 342 weight updating unit344 hopping pattern generation unit 346 hopping pattern transmissionunit 4 filter unit 400 function generation unit 402 multiplication unit406, 416 selection unit 404 LPF unit 408 selection control unit 410coefficient setting unit 412 total sum calculation unit 420 weightingunit 422 hopping pattern corresponding portion 424 delay unit 428addition unit 44 coefficient multiplication unit 440 register 442multiplication unit 444 coefficient storage unit

INDUSTRIAL APPLICABILITY

-   The present invention can be used for data transmission by spread    spectrum.

1. A communication system including a plurality of pairs of atransmitting device and a receiving device, wherein in each of thepairs, the transmitting device comprises a transmission section which,based on a spread pattern which includes a plurality of first elementsdefined with respect to components of a predetermined first number offirst domains and components of a predetermined second number of seconddomains and spreads transmission data to the components of the firstdomains and the components of the second domains, sequentially spreadstransmission data to the components of the first domains and thecomponents of the second domains every predetermined time interval andtransmits the transmission data as a transmission signal; and anupdating section which, based on the spread pattern received from thereceiving device, updates the spread pattern used to spread thetransmission data; and wherein the receiving device comprises areceiving section which receives the transmission signal; an expansionsection which sequentially expands the received transmission signal intoa plurality of second elements defined with respect to components of thefirst domains whose number is equal to or greater than the firstpredetermined number and components of the second domains whose numberis a third number which is greater than the second predetermined numberat each of the predetermined time intervals; a processing section whichsequentially performs a process using a plurality of first coefficientsdefined for each of the second elements on the second elements obtainedas a result of the expansion at each of the predetermined timeintervals; a generation unit which generates a new first coefficientusing the processed second elements and the first coefficient; selectionmeans which selects a second coefficient corresponding to the spreadpattern from within the new first coefficients as a new spread pattern;and a pattern transmission unit which transmits the new spread patternto the transmitting device.
 2. The communication system according toclaim 1, wherein the pairs include a pair of one of the transmittingdevice and the receiving device.
 3. The communication system accordingto claim 1, wherein generation of a new first coefficient by thegeneration unit of the receiving device and selection of the secondcoefficient by the selection means of the receiving device are performedrepeatedly.
 4. The communication system according to claim 1, whereinthe receiving device further comprises a decoding unit which decodes thetransmission data from the received transmission signal, and wherein thegeneration unit of the receiving device generates the new firstcoefficient so as to reduce an error rate of the decoded transmissiondata.
 5. The communication system according to claim 1, wherein areceiving section of the receiving device in one of the pairs mayreceive a transmission signal from another pair of the pairs, and thegeneration section of the receiving device generates the new firstcoefficient so as to reduce an effect of a received signal from theother pair of the pairs.
 6. The communication system according to claim1, wherein the expansion section of the receiving device performs afirst expansion process of sequentially expanding the receivedtransmission signal into third elements corresponding to the componentsof the first domains every time interval and a second expansion processof sequentially expanding the expanded third elements into the secondelements corresponding to the components of the second domains everytime interval.
 7. The communication system according to claim 6, whereinthe first domain is a frequency domain, and the first expansion processof the expansion unit of the receiving device expands the receivedtransmission signal into the third elements by separating the signalinto components of the frequency domains.
 8. The communication systemaccording to claim 7, wherein the second domain is a time domain, andthe second expansion process of the expansion section of the receivingdevice expands the third elements into the second elements bysequentially delaying at each of the time intervals by the timeinterval.
 9. The communication system according to claim 6, wherein thefirst coefficient and the second element are complex numbers, and theprocessing section of the receiving device performs filtering on thetransmission signal to obtain processing results using: a multiplicationprocess of sequentially multiplying each of the second elements by acomplex conjugate number of the first coefficient corresponding to eachof the second elements at each of the time intervals; a first additionprocess of sequentially adding all the multiplication resultscorresponding to the components of the second domains at each of thetime intervals; and a second addition process of sequentially adding allthe first addition results at each of the time intervals.
 10. Thecommunication system according to claim 9, wherein the third number isequal to the first number, and the selection section of the receivingdevice selects the first coefficient corresponding to the components ofthe first number of first domains and the components of the secondnumber of second domains from within the first coefficients as thesecond coefficient to generate the spread pattern.
 11. The communicationsystem according to claim 10, wherein the second domain is a timedomain, the second expansion process of the expansion section of thereceiving device expands the third elements into the second elements bysequentially delaying at each of the time intervals by the timeinterval, and the selection section of the receiving device selects thefirst coefficient multiplied by the second number of the third elementsfrom within the new first coefficients from the most delayed coefficientfrom the third elements, as the second coefficient to generate thespread pattern.
 12. The communication system according to claim 10,wherein the generation unit of the receiving device generates the newfirst coefficient using a symbol of the transmission data determinedfrom the processing results of the processing unit and the firstcoefficient.
 13. The communication system according to claim 12, whereinthe first domain is a frequency domain, the second domain is a timedomain, and the generation section of the receiving device determines asymbol of the transmission data in a complex form from the processingresults of the processing section.
 14. The communication systemaccording to claim 13, wherein the generation section of the receivingdevice subtracts the processing result of the processing unit from thesymbol of the determined transmission data, processes the subtractionresult and the first coefficient by a predetermined algorithm, andgenerates the spread pattern.
 15. The communication system according toclaim 1, wherein based on the subtraction result, the generation sectiongenerates the new spread pattern in such a manner that the symbol of thedetermined transmission data comes close to the processing result by theprocessing section.
 16. The communication system according to claim 15,wherein the generation of the first coefficient by the generation unitof the receiving device is performed repeatedly, the predeterminedalgorithm is implemented by: a process of generating a first matrixwhere a first coefficient used at a cycle of generation of the spreadpattern is associated with components of the frequency domain andcomponents of the time domain in a matrix form; a process of generatinga second matrix where the second element is associated with thecomponents of the frequency domain and the components of the time domainin a matrix form; a process of calculating a norm of the generatedsecond matrix; a process of dividing the result of multiplying thesubtraction result, the second matrix, and a predetermined coefficientby the square value of the norm; and a process of calculating a newfirst coefficient by adding the division result to the first coefficientused at a cycle of generation of the spread pattern.
 17. A transmittingdevice of a communication system including a plurality of pairs of atransmitting device and a receiving device, wherein in each of thepairs, the transmitting device comprises: a transmission unit which,based on a spread pattern which includes a plurality of first elementsdefined with respect to components of a predetermined first number offirst domains and components of a predetermined second number of seconddomains and spreads transmission data to the components of the firstdomains and the components of the second domains, sequentially spreadstransmission data to the components of the first domains and thecomponents of the second domains every predetermined time interval andtransmits the transmission data as a transmission signal; and anupdating unit which, based on the spread pattern received from thereceiving device, updates the spread pattern used to spread thetransmission data; and wherein the receiving device is configured to:receive a transmission signal from the transmitting device, sequentiallyexpand the received transmission signal into a plurality of secondelements defined with respect to components of the first domains whosenumber is equal to or greater than the predetermined first number andcomponents of the second domains whose number is a third number which isgreater than the predetermined second number at each of thepredetermined time intervals, sequentially perform a process using aplurality of first coefficients defined for each of the second elementson the second elements obtained as a result of the expansion at each ofthe predetermined time intervals, generate a new first coefficient usingthe processed second elements and the first coefficient, select a secondcoefficient corresponding to the spread pattern from within the newfirst coefficients as a new spread pattern; and transmit the new spreadpattern to the transmitting device.
 18. A receiving device of acommunication system including a plurality of pairs of a transmittingdevice and a receiving device, wherein in each of the pairs, based on aspread pattern which includes a plurality of first elements defined withrespect to components of a predetermined first number of first domainsand components of a predetermined second number of second domains andspreads transmission data to the components of the first domains and thecomponents of the second domains, the transmitting device sequentiallyspreads transmission data to the components of the first domains and thecomponents of the second domains every predetermined time interval andtransmits the transmission data as a transmission signal, and based onthe spread pattern received from the receiving device, the transmittingdevice updates the spread pattern used to spread the transmission data,wherein the receiving device comprises: a receiving unit which receivesthe transmission signal; an expansion unit which sequentially expandsthe received transmission signal into a plurality of second elementsdefined with respect to components of the first domains whose number isequal to or greater than the predetermined first number and componentsof the second domains whose number is a third number which is greaterthan the predetermined second number at each of the predetermined timeintervals; a processing unit which sequentially performs a process usinga plurality of first coefficients defined for each of the secondelements on the second elements obtained as a result of the expansion ateach of the predetermined time intervals; a generation unit whichgenerates a new first coefficient using the processed second elementsand the first coefficient; selection means which selects a secondcoefficient corresponding to the spread pattern from within the newfirst coefficients as a new spread pattern; and a pattern transmissionunit which transmits the new spread pattern to the transmitting device.19. A communication method for a communication system including aplurality of pairs of a transmitting device and a receiving device,wherein in each of the pairs, based on a spread pattern which includes aplurality of first elements defined with respect to components of apredetermined first number of first domains and components of apredetermined second number of second domains and spreads transmissiondata to the components of the first domains and the components of thesecond domains, the transmission device sequentially spreadstransmission data to the components of the first domains and thecomponents of the second domains every predetermined time interval andtransmits the transmission data as a transmission signal, and based onthe spread pattern received from the receiving device, the transmissiondevice updates the spread pattern used to spread the transmission data,wherein the receiving device receives the transmission signal,sequentially expands the received transmission signal into a pluralityof second elements defined with respect to components of the firstdomains whose number is equal to or greater than the predetermined firstnumber and components of the second domains whose number is a thirdnumber which is greater than the predetermined second number at each ofthe predetermined time intervals, sequentially performs a process usinga plurality of first coefficients defined for each of the secondelements on the second elements obtained as a result of the expansion ateach of the predetermined time intervals, generates a new firstcoefficient using the processed second elements and the firstcoefficient, selects a second coefficient corresponding to the spreadpattern from within the new first coefficients as a new spread pattern,and transmits the new spread pattern to the transmitting device.
 20. Anon-transitory computer-readable medium for a communication systemincluding a plurality of pairs of a transmitting device having acomputer and a receiving device, wherein the non-transitorycomputer-readable medium includes computer-readable instructions storedtherein that, upon execution by the computer, causes the transmittingdevice to perform operations comprising: based on a spread pattern whichincludes a plurality of first elements defined with respect tocomponents of a predetermined first number of first domains andcomponents of a predetermined second number of second domains andspreads transmission data to the components of the first domains and thecomponents of the second domains, sequentially spreading transmissiondata to the components of the first domains and the components of thesecond domains every predetermined time interval and transmitting thetransmission data as a transmission signal, and based on the spreadpattern received from the receiving device, updating the spread patternused to spread the transmission data; and wherein the receiving deviceis configured to: receive the transmission signal from the transmittingsignal, sequentially expands the received transmission signal into aplurality of second elements defined with respect to components of thefirst domains whose number is equal to or greater than the predeterminedfirst number and components of the second domains whose number is athird number which is greater than the predetermined second number ateach of the predetermined time intervals, sequentially perform a processusing a plurality of first coefficients defined for each of the secondelements on the second elements obtained as a result of the expansion ateach of the predetermined time intervals, generate a new firstcoefficient using the processed second elements and the firstcoefficient, select a second coefficient corresponding to the spreadpattern from within the new first coefficients as a new spread pattern,and transmit the new spread pattern to the transmitting device.
 21. Anon-transitory computer-readable medium for a communication systemincluding a plurality of pairs of a transmitting device and a receivingdevice having a computer, wherein, based on a spread pattern whichincludes a plurality of first elements defined with respect tocomponents of a predetermined first number of first domains andcomponents of a predetermined second number of second domains andspreads transmission data to the components of the first domains and thecomponents of the second domains, the transmitting device sequentiallyspreads transmission data to the components of the first domains and thecomponents of the second domains every predetermined time interval andtransmits the transmission data as a transmission signal, and based onthe spread pattern received from the receiving device, the transmittingdevice updates the spread pattern used to spread the transmission data,wherein the non-transitory computer-readable medium includescomputer-readable instructions stored therein that, upon execution bythe computer, causes the receiving device to perform operationscomprising: receiving the transmission signal; sequentially expandingthe received transmission signal into a plurality of second elementsdefined with respect to components of the first domains whose number isequal to or greater than the predetermined first number and componentsof the second domains whose number is a third number which is greaterthan the predetermined second number at each of the predetermined timeintervals; sequentially performing a process using a plurality of firstcoefficients defined for each of the second elements on the secondelements obtained as a result of the expansion at each of thepredetermined time intervals; generating a new first coefficient usingthe processed second elements and the first coefficient; selecting asecond coefficient corresponding to the spread pattern from within thenew first coefficients as a new spread pattern; and transmitting the newspread pattern to the transmitting device.